I have a layer of dirt, a layer of gravel, my rocks and then the suBwassertang is just loose on top of that. I also have some on top of my little homemade rock cave, but between the rocks, the microsword & the hygros, the suBwassertang "floats" (it rests on top of them... doesn't actually float) and leaves some spaces for the shrimp to hide in. Alpha can often be seen swimming under/through it, however, because he's a weirdo like that, LMAO.